This invention pertains to creation of electrical coronas, and in particular to an electrode arrangement for creation of a corona for surface treating of plastics and other materials.
Many plastics, when molded, will not accept an adhesive, a coating, or various inks or printing vehicles without alteration of the surface to which such materials are applied. Accordingly, surfaces are roughened or are treated with a corona in order to increase the surface wetting capability of the plastic material, and therefore its ability to accept such materials.
In the past, when plastic materials were to be treated with a corona, the corona was created by applying electricity of a sufficiently high voltage and frequency to a wire, and the plastic item was passed directly beneath the wire over an appropriate ground plane which tends to draw the corona emitted from the wire toward to the plastic object being passed beneath the wire. However, the wire naturally emits a corona irregularly, in all directions, and therefore the corona being emitted from the wire many times cannot extend a sufficient distance from the wire to treat the depths of grooves, holes and other irregularities formed in the plastic material which is desired to be treated. Because the corona is emitted in all directions, a good portion of the corona is wasted, never coming into contact with the plastic material which is to be treated.